BILBAO, Spain — A Spanish riot police officer died of cardiac arrest after clashes involving Russian soccer fans before a Europa League match on Thursday between hosts Athletic Bilbao and Spartak Moscow, raising concerns less than four months before the World Cup in Russia.

Basque Country authorities in northern Spain said the officer died in a hospital after the confrontations outside San Mames Stadium in the city of Bilbao, which will host matches in the 2020 European Championship.

Police also said a Russian man was injured but the extent of his injuries was not immediately disclosed. Five people were arrested — three Russian nationals and two Spaniards.

The identity of the dead officer was not immediately disclosed. Local media said he was a 50-year-old man.

There were conflicting reports about what caused his death, with some saying he was taken ill during the confrontations and other reports suggesting he was hit by an object during the fighting.

Spartak won the match 2-1 but Athletic advanced 4-3 on aggregate.

Earlier Thursday, German police arrested a Russian suspected of seriously injuring a British soccer fan during the European Championship in France two years ago.

"UEFA strongly condemns the violent clashes which occurred in Bilbao," the governing body for European soccer said in a statement. "We are in contact with local authorities to obtain further information on these incidents."

The Spanish league said it "deplores and condemns the death" of the police officer, and its president said he hopes FIFA and UEFA take action to halt fan violence.

"The Russian ultras shouldn't have traveled to Bilbao because of their history," Javier Tebas told the sports daily As.

The trouble erupted ahead of the round-of-32 match in the second-tiered European club competition.

Police were escorting some Spartak fans into the stadium but a stray group allegedly started igniting fireworks and throwing flares and objects toward Athletic supporters and police officers.

The fighting spread onto the streets near the stadium and police struggled to restore order. Many fans were seen trying to run away from the trouble as fireworks exploded all around.

There was concern ahead of the match because of the reported presence of 'Ultra' Russian fans in Bilbao, and a large police force was deployed to try to prevent fan trouble.

There were reports of other minor clashes involving Russian fans in Bilbao for Thursday's match.

Six years ago a fan died in Bilbao in clashes after a match between Athletic and German club Schalke.